Cool idea: gravity powered LED light
 

The wonders that are LEDs have allowed us to do some pretty cool things like make the shaker and crank flashlights. Well, a company has made another pretty cool LED light that uses gravity to power an LED lamp/light. You basically hang the lamp and then hang a weight off of it. The weight spins a generator and provides power to the lamp. To recharge the lamp, you simply lift the weight back up. Its only a few pounds, so its real easy to do. The gravity light can also be hooked up to other things to recharge them. Its pretty cheap too. Pretty cool idea IMO. :thumbup:

GravityLight: the low-cost lamp powered by sand and gravity | Art and design | guardian.co.uk

http://static.guim.co.uk/sys-images/...vitylight1.jpg

Looking at this, there has to be a somewhat simple way of calculating how much energy is stored in X weight at Y height. Anyone know what that might be?

Indeed it's quite simple: E = m * g * h
E = energy (measured in joules)
m = mass (in kilograms)
h = height (in meters)
g = gravity acceleration (about 9.81 m/s^2 (at sealevel), often rounded to 10m/s^2).

So a weigth of 0,1kg (3.53oz) dropping down 1m (3.28') gives you 1 joule of energy, which is 1 watt/h for the duration of 1 second.
If you take a weight of 4 pounds (1,8kg) and raise it 1 meter 10 times and store the energy from dropping it down you now have 18J stored, with that you can let a 0,5W lightbulb shine for 36 seconds (E = 1,8 * 10 * 1 = 18J).

This formula is the same for hydroelectric plants, that is why the dam needs to be high and there has to be a lot of water. 1 megawatt = 100m3/s * 10m *g = 5m3/s * 200m *g.

Haha, yes that is indeed a humbling formula! So much weight, or height is required to get so little power (compared to what we use daily). Its pretty crazy.

I missed this until today - the inventor was on Science Friday just now:

Inventors Design Lamp Powered Entirely by Gravity

They will be doing a crowd funding, where if you want one, you essentially pay for two, and they donate one to a deserving person in a place where they live off the grid.